A large and growing number of applications require porphyrinic macrocycles that are water-soluble and are suited for conjugation in a variety of formats. The applications encompass flow cytometry, cellular and whole-organism imaging, sensing, photodynamic therapy, biomimetic catalysis, and radical scavenging. The success of these applications relies on a host of factors, including (1) significant solubility in aqueous saline solutions, thereby avoiding intermolecular aggregation (and excited-state quenching), (2) minimal non-specific binding to cellular components, (3) incorporation of a single reactive group for conjugation, thereby avoiding crosslinking and mixtures of products, and (4) robust synthesis affording ample quantities for experimentation.